Conductive conductivity sensors are applied in varied applications for measuring conductivity of a medium.
The most well-known conductive conductivity sensors are the two electrode sensors and the four electrode sensors.
Two electrode sensors have two electrodes immersed in the medium in measurement operation and supplied with an alternating voltage. A measuring electronics connected to the two electrodes measures an electrical impedance of the conductivity measurement cell, from which then, based on an earlier determined cell constant, which depends on the geometry and other properties of the measuring cell, a specific resistance, or a specific conductance, of the medium located in the measuring cell is ascertained.
Four electrode sensors have four electrodes immersed in the medium in measurement operation, of which two are operated as so called electrical current electrodes and two as so called voltage electrodes. Applied between the two electrical current electrodes in measurement operation is an alternating voltage, which leads to an alternating electrical current flowing through the medium. The electrical current effects a potential difference between the voltage electrodes, which is determined by a preferably currentless measurement. Also in this case, by means of a measuring electronics connected to the electrical current- and voltage electrodes, the impedance of the conductivity measurement cell resulting from the supplied alternating electrical current and the measured potential difference is determined, from which then, based on an earlier determined cell constant, which depends on the geometry and other properties of the measuring cell, a specific resistance, or a specific conductance, of the medium located in the measuring cell is determined.
In conductivity sensors of today, it is not possible to detect an electrode break. This means that the user cannot always be sufficiently sure concerning the functional ability of the sensor. It is furthermore not possible to distinguish whether the sensor is located in air or whether the line to the electrodes from an evaluating electronics is interrupted.